Melatonin Secretion and Muscle Strength in Elderly Individuals: A Cross-Sectional Study of the HEIJO-KYO Cohort.

BACKGROUND

Decreased muscle strength is associated with functional limitation and disability and is a predictor of cardiovascular and all-cause mortality. Recently, oxidative stress and inflammation have been shown to contribute to the loss of muscle strength, and although melatonin has antioxidative and anti-inflammatory properties, the association between melatonin secretion and muscle strength remains unclear.

METHODS

In this cross-sectional study of 760 community-based elderly individuals (mean age, 71.0 years), we measured overnight urinary 6-sulfatoxymelatonin excretion (UME) and grip strength and quadriceps strength.

RESULTS

Median UME was 7.0 μg (interquartile range, 4.2-11.1), and mean grip and quadriceps strength were 27.5±8.4kg and 162.6±80.1 Nm, respectively. On dividing participants into quartiles by their UME level (lowest-highest UME, Q1-Q4), higher quartiles were significantly associated with increased grip strength and quadriceps strength (p for trend < .001, both). Multivariable analyses adjusted for potential confounders (age, gender, body mass index, smoking and drinking statuses, renal function, hypertension, diabetes, physical activity, depressed mood, cognitive impairment, bedtime, sleep duration, and day length) revealed that both grip and quadriceps strength were significantly increased in Q4 compared with that in Q1 (adjusted mean difference, Q4 - Q1: grip strength, 1.5kg; 95% confidence interval [CI], 0.4-2.6kg; p = .006; quadriceps strength, 14.2 Nm; 95% CI, 1.3-27.1 Nm; p = .031).

CONCLUSIONS

Melatonin secretion was significantly associated with muscle strength in this elderly population. Further longitudinal studies are needed to ascertain the effect of melatonin levels on muscle strength.